I'm using code from the pymunk index_video to create a generic function that creates multiple cars which race each other and if they reach the right extreme of the screen, they are removed from Space and re-generated on the left extreme of the screen.
The problem is, that in the example code, each part of the car (chassis, pin joint, motor, wheels) is added to Space separately. I wanted to treat the entire car as a single body whose coordinates I can keep track of by storing the reference of the entire car body in a List and add or delete it to the Space easily.
Also, if the wheels are too close to the chassis, they collide with each other. I presume using a ShapeFilter can help avoid such collisions, but for that I need all parts of the car as a single body.
Please bear with me. I'm completely new to this jargon.
def car(space):
pos = Vec2d(100,200)
wheel_color = 52,219,119
shovel_color = 219,119,52
mass = 100
radius = 25
moment = pymunk.moment_for_circle(mass, 20, radius)
wheel1_b = pymunk.Body(mass, moment)
wheel1_s = pymunk.Circle(wheel1_b, radius)
wheel1_s.friction = 1.5
wheel1_s.color = wheel_color
space.add(wheel1_b, wheel1_s)
mass = 100
radius = 25
moment = pymunk.moment_for_circle(mass, 20, radius)
wheel2_b = pymunk.Body(mass, moment)
wheel2_s = pymunk.Circle(wheel2_b, radius)
wheel2_s.friction = 1.5
wheel2_s.color = wheel_color
space.add(wheel2_b, wheel2_s)
mass = 100
size = (50,30)
moment = pymunk.moment_for_box(mass, size)
chassi_b = pymunk.Body(mass, moment)
chassi_s = pymunk.Poly.create_box(chassi_b, size)
space.add(chassi_b, chassi_s)
vs = [(0,0),(25,45),(0,45)]
shovel_s = pymunk.Poly(chassi_b, vs, transform = pymunk.Transform(tx=85))
shovel_s.friction = 0.5
shovel_s.color = shovel_color
space.add(shovel_s)
wheel1_b.position = pos - (55,0)
wheel2_b.position = pos + (55,0)
chassi_b.position = pos + (0,-25)
space.add(
pymunk.PinJoint(wheel1_b, chassi_b, (0,0), (-25,-15)),
pymunk.PinJoint(wheel1_b, chassi_b, (0,0), (-25, 15)),
pymunk.PinJoint(wheel2_b, chassi_b, (0,0), (25,-15)),
pymunk.PinJoint(wheel2_b, chassi_b, (0,0), (25, 15))
)
speed = 4
space.add(
pymunk.SimpleMotor(wheel1_b, chassi_b, speed),
pymunk.SimpleMotor(wheel2_b, chassi_b, speed)
)
So this question is actually two questions.
A. How to make a "car object" that consists of multiple parts
There is no built in support for this, you have keep track of it yourself.
One way to do it is to create a car class that contains all the parts of the car. Something like this (not complete code, you need to fill in the full car)
class Car():
def __init__(self, pos):
self.wheel_body = pymunk.Body()
self.wheel_shape = pymunk.Circle()
self.chassi_body = pymunk.Body()
self.chassi_shape = pymunk.Poly()
self.motor = pymunk.SimpleMotor(wheel_body, chassi_body, 0)
def add_to_space(self, space)
space.add(self.wheel_body, self.wheel_shape, self.chassi_body, self.chassi_shape, self.motor)
def set_speed(self, speed)
self.motor.rate = speed
def car_position(self)
return self.chassi_body.position
B. How to make parts of the car to not collide with each other
This is quite straight forward, just as you already found the ShapeFilter is the way to go. For each "car", create a ShapeFilter and set a unique non-zero group on it. Then set that ShapeFilter as the filter property on each shape that makes up the car. It doesnt matter if the shapes belong to the same body or not, any shape with a ShapeFilter with a group set will not collide to other shapes with the same group set.
Related
Can someone suggest how I can vary the UIPushBehavior magnitude force by distance from source. To mirror the affect of the force of wind from a fan on another object. So the closer the object is to the fan the stronger the force.
if String(describing: identifier) == "fan1" {
self.push = UIPushBehavior(items: [self.object], mode: .instantaneous)
self.push.setAngle(.pi/4, magnitude: 1)
self.animator.addBehavior(self.push)
self.push.addItem(self.object)
}
Use a UIFieldBehaviour to create a linear gravitational field in the direction of the fan. Then you can specify a falloff:
var forceField: UIFieldBehaviour!
// ...
forceField = UIFieldBehavior.linearGravityField(direction: CGVector(dx: 1, dy: -5))
// example values for a "fan" on the bottom left blowing mostly upwards:
forceField.position = CGPoint(x: view.bounds.minX, y: view.bounds.maxY)
forceField.region = UIRegion(radius: 3000)
forceField.minimumRadius = 100
forceField.falloff = 5
forceField.strength = 10
forceField.addItem(view1)
forceField.addItem(view2)
animator.addBehavior(forceField)
Have fun playing around with these values!
Adding collision, another gravity behaviour, and a dynamic item behaviour to two views, we get the following effect:
That feels like a fan on the bottom left to me!
You can also choose a radial gravitational field positioned at where the fan is, if your fan is in a corner and blows "radially", but note that you should use a negative value for strength in that case to say that the field repels rather than attracts.
I've been trying to implement an infinite background animation, which should change between 4 images of equal height and then repeat the sequence. However, it does not seem to work properly.
Note anchorPoint = CGPoint(x: 0.5, y: 0)
func updateBackground(currentTime: TimeInterval){
var delta: CGFloat = 0.0
if lastUpdate != nil {
delta = CGFloat(currentTime - lastUpdate)
}
//First increment position
activeBackground1.position.y += delta*backgroundVelocity
activeBackground2.position.y += delta*backgroundVelocity
//Detect bounds surpass
if activeBackground1.position.y > activeBackground1.size.height + screen.height/2 {
lastSky = (lastSky + 1)%4
sky1 = SKTexture(imageNamed: "sky" + String(lastSky))
activeBackground1.texture = sky1
//Reposition: background1 new position is equal to minus the entire height of
//background2 + its y size.
activeBackground1.position.y = -abs(activeBackground2.size.height-activeBackground2.position.y)
}
if activeBackground2.position.y > activeBackground2.size.height + screen.height/2 {
lastSky = (lastSky + 1)%4
sky1 = SKTexture(imageNamed: "sky" + String(lastSky))
activeBackground2.texture = sky1
activeBackground2.position.y = -abs(activeBackground1.size.height-activeBackground1.position.y)
}
}
The update algorithm works fine, but when it is needed to reposition one of the two background, it seems there is an offset of about 10.0 CGFloat from one background to another. What am I doing wrong?
EDIT: It turned out that the error was located in my image, which presented some blank rows and therefore generated visualisation glitches. So my code works perfectly.
I do the test and most likely you should use something like:
activeBackground2.position.y = activeBackground1.size.height + activeBackground1.position.y
instead of
activeBackground2.position.y = -abs(activeBackground1.size.height-activeBackground1.position.y)
I did this example and it works correctly: https://github.com/Maetschl/SpriteKitExamples/tree/master/InfiniteBackground/InfiniteBackground
Feel free to see and use.
Your problem is floating point math causing rounding errors. I am on a phone right now so I can’t wrote code, but what you want to do is have 1 parent SKNode to handle your entire background.
Add your background slivers to the parent node.
You then place the moving action on the parent only.
As each sliver leaves the screen, you take the sliver, and move it to the end of the other slivers.
This jumping should always be done with integer math, leaving no holes.
Basically:
The floating point moving math is done on the parent node.
The integer based tile jumping is done on each of the slivers.
I have a game with a character who is affected by normal gravity as he jumps across platforms. He collects coins and power ups. I'm making a power up that makes coins gravitate to the characterSpriteNode.
In the case that magneticPowerUp = true I want it to appear that a gravitational field has activated about the character that makes only the coins attract to the character, like a magnetic field.
I've been fideling with Epic Bytes SO answer here but i'm not having much luck as i don't have much experience with vectors and haven't got too deep into physicsBody.
So I just can't work out the part that will make the coins move once it has decided the coin is close enough to move to the char.
My thoughts are something like this:
override func update(currentTime: NSTimeInterval) {
if magneticPowerUp {
for coin in scoreNode.children {
let disp = CGVector(dx: coin.position.x-character.position.x, dy: coin.position.y-character.position.y)
let radius = sqrt(disp.dx*disp.dx+disp.dy*disp.dy) // Distance between character and coin
if radius < character.frame.height * 3 {
// Use physics methods here to push the coin to the character
let dt: CGFloat = 1.0/60.0
let strength: CGFloat = 10000
let m1 = character.physicsBody!.mass*strength
let m2 = coin.physicsBody!.mass*strength
let force = (m1*m2)/(radius*radius);
let normal = CGVector(dx: disp.dx/radius, dy: disp.dy/radius)
let impulse = CGVector(dx: normal.dx*force*dt, dy: normal.dy*force*dt)
// Something wrong with this?
coin.physicsBody!.velocity = CGVector(dx: coin.physicsBody!.velocity.dx + impulse.dx, dy: coin.physicsBody!.velocity.dy + impulse.dy)
}
}
}
}
SpriteKit has SKFieldNode for creating gravity and magnets that apply to bodies. Normally it deflects charged bodies instead of attracting them like ferromagnetism in the real world.
If you want a field that attracts things you'll need a radialGravityField() method around your hero. To attract specific things like your coins you would use categoryBitMask on the hero field and fieldBitMask on the coin sprites you want to attract.
With the electricField() method you could also have your hero attract different bodies with stronger or weaker forces. Or even attract and repel different bodies at the same time. You can use the charge property of physics bodies.
Code examples:
var field:SKFieldNode?
switch( name )
{
case .Electric:
var electric = SKFieldNode.electricField()
electric.strength = 100.0
bestBodyMass = 0.5
impulseMultiplier = 400
field = electric
case .Magnetic:
var magnetic = SKFieldNode.magneticField()
magnetic.strength = 1.0
bestBodyMass = 0.5
impulseMultiplier = 400
field = magnetic
}
The Apple documentation for SKFieldNode is awesome.
https://developer.apple.com/reference/spritekit/skfieldnode
Here's are two cool YT videos showing the effect.
https://www.youtube.com/watch?v=-mjRPgP0oAE
https://www.youtube.com/watch?v=JGk3agy-c50
Thanks in advance. I currently have a sprite controlled by the tilting of the device and would like every so often(NSTimer) for another sprite to appear behind it following it with the same physics. I have it set up, but i need the position to update every second so it follow behind it. How would I go about this? This is what I've tried/done.
let snakeBodyY = snakeHead.position.y - 5
let snakeBodyX = snakeHead.position.x - 5
snakeHead = SKSpriteNode(imageNamed: "snakeHead")
snakeHead.size = CGSize(width: 60, height: 60)
snakeHead.position = CGPoint(x: self.frame.midX, y: self.frame.midY - 50)
self.addChild(snakeHead)
snakeBody = SKSpriteNode(imageNamed: "snakeBody")
snakeBody.size = CGSize(width: 50, height: 50)
snakeBody.position.x = snakeBodyX
snakeBody.position.y = snakeBodyY
self.addChild(snakeBody)
Depends on how advance you need it,
if this is a free range 2D world you could assign the each new body to the tail so that the positions are relative to the snake, and always try to make the body parts move to the center of the previous body part up to the head.
Set up your sprite like this:
let snake = SKNode...
let head = SKSpriteNode...
let tail = SKSpriteNode...
//make sure you set up your positions for each body part, they should be relative to snake, not the screen
//setup collision so that tail and head can collide
head.physicsBody = SKPhysicsBody...
head.categoryBitMask = 1
head.collisionBitMask = 1
tail.physicsBody = SKPhysicsBody...
tail.categoryBitMask = 1
tail.collisionBitMask = 1
//setup restitution so that they do not bounce when colliding
head.restitution = 0
tail.restitution = 0
//add the parts to snake
snake.addChild(head)
snake.addChild(tail)
//Now you have a snake with a head and tail create an action to move the snake tail to the center of head
let moveToCenter = SKAction.moveTo(head.position, duration:0)
tail.runAction(moveToCenter)
//this will move the talk to try to get to the center of head, but collision physics will stop it from overlapping.
//Now everytime you want to add a new body
let body = SKSpriteNode...
body.physicsBody = SKPhysicsBody...
body.categoryBitMask = 1
body.collisionBitMask = 1
body.restitution = 0
snake.addChild(body)
let moveToCenter = SKAction.moveTo(tail.position, duration:0)
body.runAction(moveToCenter)
tail = body //lets make the tail the new piece to add
//Then on every update loop. you want to go through the children and do something like this
let previousChild = head
for child in snake.children
{
if child == head
{
continue;
}
child.removeAllActions()
let moveToCenter = SKAction.moveTo(previousChild.position, duration:0)
child.runAction(moveToCenter)
previousChild = child
}
Now if you find that this code may end up running slow for you, and don't mind a more stiff approach, you could also look up SKAction.followPath. Now I am not going to get into the details here, but basically what you need to do is record how your snake moves, then you generate a path with it, and use SKAction.followPath to make all the body parts move along the path.
If you are working in a 2d tiled world that only allows vertical and horizontal movement, you create an array of your sprites, and every time your snake makes a movement, you go down the snake and change its position to the previous body parts position
I'm trying to write an object oriented program (as a learning exercise, I know there may be simpler ways to do it) in which beads bounce around a 2D plane bounded by a ring. Each bead is an object defined by a class ball. In setting the initial positions of the balls I need to check that no other ball has already been placed at the same x and y coordinates.
#Class for the beads
class ball:
NumbBalls = 0
#Constructor
def __init__(self,Beads):
self.ball = sphere(pos = vector(0,0,0), radius = radiusBall,color=color.red)
ball.NumbBalls += 1
self.ball.pos = self.createInitialPosition(Beads)
#Assign ball its initial position
def createInitialPosition(self,other):
#CODE to compare self.ball.pos and other.ball.pos which returns a unique position coordinate
#Main program
NumbBeads = 100
Beads = []#Create empty list for all the beads
#create balls in random initial positions
Beads = [ball(Beads) for item in range(NumbBeads)]
I can get this to work if I create two objects bead1 and bead2 and then pass bead1 and bead2 as arguments ie bead2 = ball(bead1) but how do I do this if I am generating a list of beads and want all of them to be compared with self. Hopefully that makes sense.
Perhaps rather than the approach you are currently taking, you should consider something along these lines (of course, with the necessary changes to your class definition/methods):
N = 100
initialPositions = []
while len(initialPositions) <= N:
newPosition = generateRandomPosition()
if newPosition in initialPositions:
pass
else:
initialPositions.append(newPosition)
ballList = [ ball(p) for p in initialPositions ]
In other words, generate a list of initial positions outside of the creation of your objects, and do whatever validation/restriction you need during that creation. Then just create your objects from that list. If N is really large, you might want to consider a dictionary (or a mutable set of some sort) instead of a list for initialPositions, to help speed up the membership testing, but it's still the same concept...